Is there any objective investigation into who actually shot them down? (I'm asking honestly)
3 weeks before MH-17, rebels captured a full Ukrainian military installation containing a number of BUK missile systems and parts storage for them. They were able to repair one BUK launcher. There is no need for an electronics professional like Kerry suggested because Russian military system like BUK is repaired by swapping whole blocks (sourced from other launchers or from parts storage). A BUK launcher is only part of the system. It has smaller, less capable fire control radar (lesser range, only 120 degree instead of 360, lesser resolution) than the main BUK radar (which is a large radar on a separate vehicle, has full acquiring/identifying/tracking/targeting capabilities, and rebels didn't have a working one). Basically BUK launcher alone is a super-large glorified "Stinger". Using the repaired launcher, 2 weeks after capture, the rebels downed 2 Ukrainian transport planes and week later they celebrated, for half-an-hour, until the first people reached the crash site, the supposed downing of the 3rd transport plane.
Russia obviously doesn't want the public confirmation because it was Russia supported rebels who downed the plane. US/Ukraine don't want it because it was a BUK captured from Ukrainians, and Ukraine hadn't close the airspace and was accepting the civilian airliners' flight plans through the war zone (basically each time declare it safe to fly) even though the Ukrainian military were regularly flying the combat missions in the airspace, receiving anti-aircraft fire and losing planes to it, lost a number of BUK systems to rebels, after that lost 2 cargo planes to surface-to-air missiles at the heights not reachable by MANPAD missiles - and still didn't close the airspace and were still explicitly accepting civilian flight plans... This is why all this propaganda theories about a ghost lone Russian BUK launcher almost every night crossing into Ukraine territory and crossing back again.